This invention relates to a method for separating uranium from thorium. More specifically, this invention relates to a method for separating uranium from a mixture of thorium and uranium oxides.
In order to meet the ever increasing demand for energy with limited natural resources, considerable work has been done throughout the world on the development of breeder reactors. Because of the larger and cheaper resources of thorium in comparison to uranium, interest has been stimulated in Th-U-233 fuel cycle. In this cycle, U-233 is bred by neutron capture and beta decay. U-233 is a better fissile material than U-235 and it is expected that Th-U-233-fueled reactors can produce energy at a lower price than does a U-235-fueled reactor.
One of the disadvantages of the thorium cycle is that the reprocessing of thorium-based fuel is more difficult in comparison to that of uranium-based fuel, if the same facilities are to be used. However, if a nonaqueous reprocessing method is developed, which in general is more compact and involves a smaller number of chemical steps, the thorium fuel cycle may become still more attractive. A wide variety of nonaqueous methods have been developed for reprocessing of different types of nuclear fuels. Many of these processes involve oxidation-reduction reactions in the presence of fused salts and, because of their similarity to pyrometallurgical methods used in extraction of metals, these reprocessing methods have been called pyrometallurgical reprocessing methods.
In the early stages of the development of the thorium cycle, metallic fuel was under consideration. A pyrometallurgical process was developed which involves oxidation-reduction reactions in a fused salt-liquid metal system and the transfer of solutes from one alloy phase to the other through a fused salt phase.
However, the recent trend is towards ceramic fuel and considerable work has been done on the oxide fuels. Some of the breeder reactors are being planned for an oxide fuel consisting of UO.sub.2 dissolved in ThO.sub.2. The (Th,U)O.sub.2 prepared by the sol-gel process is extremely inert in aqueous mediums and sol-gel ThO.sub.2 has been found to react slowly in the presence of fused salt bath. Thus, a pyrometallurgical reprocessing method becomes still more desirable for (Th,U)O.sub.2 fuels.
The pyrometallurgical method developed for separation of metallic uranium and thorium may be used for oxides if the oxides are reduced to metals in a preliminary step. This approach has been used for (U,Pu)O.sub.2 fuels. Fused salt-liquid metal systems have been developed for the reduction of UO.sub.2 and ThO.sub.2. However, it has been noted that the reduction of sol-gel ThO.sub.2 fired at 650.degree.C. is very difficult and some preliminary work has indicated that dense sol-gel ThO.sub.2 pellets fired at 2800.degree.C. cannot be reduced by this method.